ITU‐T's Technical Reports and Specifications 611 Complex or shared base stations Antennas are often grouped together on masts. The combination illustrated here is that of an omnidirectional antenna mounted above a cluster of three sector antennas. In the case that multiple antennas are present on a site, whenever an additional antenna is installed, the compliance boundary of each antenna should be evaluated again, taking into account the additional exposure of the newly installed antenna. In the diagram, the compliance boundaries are shown independently for each antenna. For antennas that are close together or operate at high powers, the zones may overlap leading to large exclusion zones than for the individual antennas. Small cells Small cells are low‐powered radio access nodes that operate in licensed or unlicensed spectrum that have a range of a few meters up to 1 to 2 kilometres. Small cells can be used to provide in‐building or outdoor wireless service. They are often used to increase the network capacity and coverage in localized areas. As these are low powered devices, compliance distances are very small and may be incorporated within the antenna cover. For some sites, installation recommendations may be provided to ensure compliance with limits.